swc-project/swc · error

failed to create file ({}) for writing data of the failed as

Error message

failed to create file ({}) for writing data of the failed assertion: {}

What it means

Raised in `write_to_file` (crates/testing/src/lib.rs:222), called from print_left_right after an assertion failure. When a fixture assertion fails, the harness dumps the left/right values to files under the test-results directory; if File::create fails for that path (permission denied, read-only FS, missing parent directory, sandbox restrictions), this panic replaces the assertion output. The error from File::create, caused by an unwritable results path, is the input at fault.

Source

Thrown at crates/testing/src/lib.rs:222

            let cp = self.cm.lookup_char_pos(span.lo());

            let line = cp.line;
            let column = cp.col.0 + 1;

            line * 10000 + column
        });

        match result {
            Ok(res) => Ok(res),
            Err(()) => Err(errs),
        }
    }
}

fn write_to_file(path: &Path, content: &str) {
    File::create(path)
        .unwrap_or_else(|err| {
            panic!(
                "failed to create file ({}) for writing data of the failed assertion: {}",
                path.display(),
                err
            )
        })
        .write_all(content.as_bytes())
        .expect("failed to write data of the failed assertion")
}

pub fn print_left_right(left: &dyn Debug, right: &dyn Debug) -> String {
    fn print(t: &dyn Debug) -> String {
        let s = format!("{t:#?}");

        // Replace 'Span { lo: BytePos(0), hi: BytePos(0), ctxt: #0 }' with '_'
        let s = {
            static RE: Lazy<Regex> =
                Lazy::new(|| Regex::new("Span \\{[\\a-zA-Z0#:\\(\\)]*\\}").unwrap());

View on GitHub (pinned to 5176682b65)

Solutions

1. Check that the target directory exists and is writable before the test run (create it in advance)
2. Ensure target/swc-test-results is not locked by another process or made read-only by the environment
3. Make write_to_file degrade gracefully (e.g. print contents to stderr) so the original assertion failure is still visible

When it happens

Trigger: Thrown at crates/testing/src/lib.rs:222 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/788deabe24e8bcca. Report an issue: GitHub.